Edgedancers and Physics

[Spren of Kindness]

This morning, I woke up, and my first thought was : 'Wait, if Lift can remove friction, what happens if she Slicks, then drops, a ball?'  There's no friction - just gravity, and lower gravity at that.  Is it unbalanced force if there's just one force?  What happens to the ball?  Does it have terminal velocity?  Does it just keep accelerating until it hits the ground?  What is even going on there? 

Does someone who knows more about physics know what's going on in this situation?

[theTruthshaper]

8 minutes ago, Spren of Kindness said:

This morning, I woke up, and my first thought was : 'Wait, if Lift can remove friction, what happens if she Slicks, then drops, a ball?'  There's no friction - just gravity, and lower gravity at that.  Is it unbalanced force if there's just one force?  What happens to the ball?  Does it have terminal velocity?  Does it just keep accelerating until it hits the ground?  What is even going on there? 

Does someone who knows more about physics know what's going on in this situation?

I am not sure what you are confused about.

If Lift Slicks the ball and drops it, then it'll keep on accelerating until it hits the ground.

[Spren of Kindness]

Just now, The_Truthwatcher said:

I am not sure what you are confused about.

If Lift Slicks the ball and drops it, then it'll keep on accelerating until it hits the ground.

I thought so, but I was sleep-addled and couldn't remember science class.  I'm mostly confused because Radiants are breaking the laws of physics and so I have to sort through what I know and figure out what applies, what doesn't, and how those changes affect things.

[Ixthos]

6 minutes ago, Spren of Kindness said:

I thought so, but I was sleep-addled and couldn't remember science class.  I'm mostly confused because Radiants are breaking the laws of physics and so I have to sort through what I know and figure out what applies, what doesn't, and how those changes affect things.

Think of it like the experiment of dropping a hammer and a feather on the Moon, as was done during the Apollo Program to test Galileo's theories. On Earth the hammer hits the ground first because it can push past the air more easily than the feather, the feather's surface and low weight meaning it is more subject to the interactions with air than the hammer is. On the Moon, however, the two hit the ground at the same time because there is no air - or not enough air - to interfere with the feather's fall. So, if Lift were to do this, any object she slicked would fall at the same rate as any other, as though they were in a vacuum.

[theTruthshaper]

2 minutes ago, Ixthos said:

Think of it like the experiment of dropping a hammer and a feather on the Moon, as was done during the Apollo Program to test Galileo's theories. On Earth the hammer hits the ground first because it can push past the air more easily than the feather, the feather's surface and low weight meaning it is more subject to the interactions with air than the hammer is. On the Moon, however, the two hit the ground at the same time because there is no air - or not enough air - to interfere with the feather's fall. So, if Lift were to do this, any object she slicked would fall at the same rate as any other, as though they were in a vacuum.

I am not sure about this though. Slicking will only remove the friction felt by the object, any normal force (Normal as in direction) should still act on it.

[Spren of Kindness]

10 minutes ago, Ixthos said:

Think of it like the experiment of dropping a hammer and a feather on the Moon, as was done during the Apollo Program to test Galileo's theories. On Earth the hammer hits the ground first because it can push past the air more easily than the feather, the feather's surface and low weight meaning it is more subject to the interactions with air than the hammer is. On the Moon, however, the two hit the ground at the same time because there is no air - or not enough air - to interfere with the feather's fall. So, if Lift were to do this, any object she slicked would fall at the same rate as any other, as though they were in a vacuum.

That makes sense.  Thanks!

[Aspiring Writer]

37 minutes ago, The_Truthwatcher said:

I am not sure about this though. Slicking will only remove the friction felt by the object, any normal force (Normal as in direction) should still act on it.

There is a maximum speed an object can fall at called terminal velocity regardless of friction. The ball would fall until it reached terminal velocity and then stop at that speed. The reason objects fall slower is air resistance, so once you remove that, it will simply fall with gravity as if there is no air, which has been done and recorded with a bowling ball and a feather, by the way, so I would suggest watching that to see how that looks.

Also, PHYSICS, PHYSICS, PHYSICS!

Edited November 20, 2020 by Aspiring Writer

[Ixthos]

1 hour ago, The_Truthwatcher said:

I am not sure about this though. Slicking will only remove the friction felt by the object, any normal force (Normal as in direction) should still act on it.

I see your point, but remember that the investiture could be redirecting those forces in order to allow her to be frictionless in the first place. Also remember that she previously used it to move so fast she broke the sound barrier, so ... :-P I think it actively redirects the air or other material away from her, provided it isn't too solid like a tree. [Edit: basically the air never has a chance to push against her because the investiture moves it to the side, and moving an equal amount to each side cancels out the sideways forces.]

 

1 hour ago, Spren of Kindness said:

That makes sense.  Thanks!

You are welcome :-)

Edited November 20, 2020 by Ixthos

[theTruthshaper]

1 hour ago, Aspiring Writer said:

There is a maximum speed an object can fall at called terminal velocity regardless of friction. The ball would fall until it reached terminal velocity and then stop at that speed. The reason objects fall slower is air resistance, so once you remove that, it will simply fall with gravity as if there is no air, which has been done and recorded with a bowling ball and a feather, by the way, so I would suggest watching that to see how that looks.

Also, PHYSICS, PHYSICS, PHYSICS!

Wrong. Terminal velocity is a *consequence* of friction. In a vacuum, all objects continually increase in momentum.

 

38 minutes ago, Ixthos said:

I see your point, but remember that the investiture could be redirecting those forces in order to allow her to be frictionless in the first place. Also remember that she previously used it to move so fast she broke the sound barrier, so ... :-P I think it actively redirects the air or other material away from her, provided it isn't too solid like a tree. [Edit: basically the air never has a chance to push against her because the investiture moves it to the side, and moving an equal amount to each side cancels out the sideways forces.]

Do you think that there would be no buoyant force on a Slicked object?

[Aspiring Writer]

7 minutes ago, The_Truthwatcher said:

Wrong. Terminal velocity is a *consequence* of friction. In a vacuum, all objects continually increase in momentum.

 

Do you think that there would be no buoyant force on a Slicked object?

Um, no. Terminal velocity is the fastest an object can fall when only affected by that lanet's gravity. An object cannot approach the speed of light simply because it's moving, it would need something to keep it accelerating. also, this.

In short, it would assist gravity in fighting the air resistance, and bring the body down at a faster speed. No, you cannot fall faster than terminal velocity. Why? Simply because the maximum speed you attain when falling is called terminal velocity when there is no acceleration.

Termicnal velocity is not because of air resistance. It is because of gravity. 

[theTruthshaper]

Just now, Aspiring Writer said:

Um, no. Terminal velocity is the fastest an object can fall when only affected by that lanet's gravity. An object cannot approach the speed of light simply because it's moving, it would need something to keep it accelerating. also, this.

In short, it would assist gravity in fighting the air resistance, and bring the body down at a faster speed. No, you cannot fall faster than terminal velocity. Why? Simply because the maximum speed you attain when falling is called terminal velocity when there is no acceleration.

Termicnal velocity is not because of air resistance. It is because of gravity. 

Gravity merely applies a constant force downward which continually increases the momentum.

Terminal velocity arises due to both gravity and air resistance. Gravity provides a constant downward force, air resistance provides an upward force which varies with the speed of the object. When the magnitude of the force due to air resistance becomes exactly equal to that dues to gravity, the object stops increasing in momentum. This is what we call as terminal velocity. There is no terminal velocity without air (or in the more general case fluid) resistance.

[Aspiring Writer]

11 minutes ago, The_Truthwatcher said:

Gravity merely applies a constant force downward which continually increases the momentum.

Terminal velocity arises due to both gravity and air resistance. Gravity provides a constant downward force, air resistance provides an upward force which varies with the speed of the object. When the magnitude of the force due to air resistance becomes exactly equal to that dues to gravity, the object stops increasing in momentum. This is what we call as terminal velocity. There is no terminal velocity without air (or in the more general case fluid) resistance.

You would need another force to keep it accelerating. Gravity has a certain amount of strength and can't make an object go faster at one point, otherwise Earth would be constantly increasing speed.

[theTruthshaper]

Just now, Aspiring Writer said:

You would need another force to keep it accelerating. Gravity has a certain amount of strength and can't make an object go faster at one point, otherwise Earth would be constantly increasing speed.

I think you are majorly confused about how forces work.

A constant force constantly changes the momentum of an object. The reason that the earth is not constantly increasing speed is that, the force on the earth is perpendicular to i's velocity, this makes it go around the sun, while not changing it's speed.

Essentially, any force can add an arbitrarily large momentum to an object given enough time.

[Aspiring Writer]

Just now, The_Truthwatcher said:

I think you are majorly confused about how forces work.

A constant force constantly changes the momentum of an object. The reason that the earth is not constantly increasing speed is that, the force on the earth is perpendicular to i's velocity, this makes it go around the sun, while not changing it's speed.

Essentially, any force can add an arbitrarily large momentum to an object given enough time.

An object can't go faster than the force that's moving it. There are different strengths of gravitational pull for a reason, gravity has a limit. A planet rotating perpendicular is basically infinity falling, making it a good analogy to dropping a ball that has been slicked. It will reach a speed and then stop accelerating until/unless another force acts on it to continue accelerating.

The acceleration due to gravity is ALWAYS negative. Any object affected only by gravity (a projectile or an object in free fall) has an acceleration of -9.81 m/s², regardless of the direction. 

[HSuperLee]

4 minutes ago, Aspiring Writer said:

An object can't go faster than the force that's moving it. There are different strengths of gravitational pull for a reason, gravity has a limit. A planet rotating perpendicular is basically infinity falling, making it a good analogy to dropping a ball that has been slicked. It will reach a speed and then stop accelerating until/unless another force acts on it to continue accelerating.

The acceleration due to gravity is ALWAYS negative. Any object affected only by gravity (a projectile or an object in free fall) has an acceleration of -9.81 m/s², regardless of the direction. 

Force doesn't have a speed. The different strengths of gravity are caused by mass, which does affect force, but it doesn't make the force not constant. Without air resistance, gravity's effect on an object is F = G * (M1*M2)/(r^2) where F is force, G is the universal gravitational constant, M is mass, and r is distance (technically radius but eh, same thing.) There's nothing in the equation that would cause this to have a limit to how fast an object could go. It does cause a limit to acceleration, because A=F/M, but that acceleration would be constant, and thus velocity would keep increasing with time.

 

Edit: I'm not sure I actually addressed much of what you said. But you seem to think gravity isn't a constant force. It most certainly is. You'd know if it wasn't because things would suddenly become weightless.

Edited November 20, 2020 by HSuperLee

[Aspiring Writer]

1 minute ago, HSuperLee said:

Force doesn't have a speed. The different strengths of gravity are caused by mass, which does affect force, but it doesn't make the force not constant. Without air resistance, gravity's effect on an object is F = G * (M1*M2)/(r^2) where F is force, G is the universal gravitational constant, M is mass, and r is distance (technically radius but eh, same thing.) There's nothing in the equation that would cause this to have a limit to how fast an object could go. It does cause a limit to acceleration, because A=F/M, but that acceleration would be constant, and thus velocity would keep increasing with time.

hmm. Interesting.

[theTruthshaper]

7 minutes ago, Aspiring Writer said:

An object can't go faster than the force that's moving it. There are different strengths of gravitational pull for a reason, gravity has a limit. A planet rotating perpendicular is basically infinity falling, making it a good analogy to dropping a ball that has been slicked. It will reach a speed and then stop accelerating until/unless another force acts on it to continue accelerating.

The acceleration due to gravity is ALWAYS negative. Any object affected only by gravity (a projectile or an object in free fall) has an acceleration of -9.81 m/s², regardless of the direction. 

What do you mean by the acceleration being negative? Do you mean that objects are being accelerated towards the center of the earth?

A planet rotating around a star is not a good analogy for a falling object, in this case.

A falling object will have a constant acceleration of 9.81 m/s^2 (assuming not very high speed, and close to earth). This means it's speed will be constantly increasing (while falling) by 9.81 m/s per second. There is no limit to the momentum gravity can impart to a falling object.

[Ixthos]

53 minutes ago, The_Truthwatcher said:

Do you think that there would be no buoyant force on a Slicked object?

Hmmm ... that's a good question. No, I don't think so. I think if something was completely slicked, or if there is no way to specify a direction for the slickness to apply and it applies across any direction, I think a ship for example probably would sink. Unless, of course, belief and expectation affect it, in which case then yes it would, but I imagine that if Lift were to fully slick a boat the water would slide right away from it and around it and it would sink, or if she slicked a balloon it would fall, unless she only slicked the front of the boat, or the top of a balloon.

[theTruthshaper]

2 minutes ago, Ixthos said:

Hmmm ... that's a good question. No, I don't think so. I think if something was completely slicked, or if there is no way to specify a direction for the slickness to apply and it applies across any direction, I think a ship for example probably would sink. Unless, of course, belief and expectation affect it, in which case then yes it would, but I imagine that if Lift were to fully slick a boat the water would slide right away from it and around it and it would sink, or if she slicked a balloon it would fall, unless she only slicked the front of the boat, or the top of a balloon.

But we know that changing friction does not change the buoyant force.

[Ixthos]

1 minute ago, The_Truthwatcher said:

But we know that changing friction does not change the buoyant force.

This isn't fully about friction any more than adhesion is fully about pressure. Basically the way I see it is that the abrasion prevents the material it presses against from exerting a force on the object it covers if the material itself isn't solid, instead it moves it around the material, pushing it to the sides. Buoyancy works because the pressure on the sides of an object near the top are slightly weaker than the pressure below, but this still requires the material to apply pressure to the surface area of the object. If the effectively move every particle that "would" touch an object away from it, they can't apply a force to it, so it wouldn't be buoyed up.

Put it this way: when Lift was sliding along and broke the sound barrier, what was the air doing directly in front of her?

[Jaconis]

To those above, I believe the confusion is arriving due to the difference between acceleration and velocity.

Velocity is the measure of an object’s change in position relative to time, that is to say, how fast the object is moving. Its measured in units of length/time (miles per hour, feet per second, km per hour, etc.)

Acceleration is the measure of an objects change in velocity relative to time, that is to say, how quickly is the speed of an object changing. It’s measured in units of (length/time)/time or length/time^2 (feet per second^2). 

Force is equal to mass x acceleration. 

Gravity and wind resistance are both forces, meaning we are dealing with accelerations here. As was pointed out above, the force due to wind resistance increases with velocity. This means that, in a free fall, the acceleration due to the gravity force will continue to increase velocity, increasing wind resistance until the force due to wind resistance is equal to the gravity force, resulting in a net zero force on the object and thus no acceleration and no further increase in velocity. This is called terminal velocity, and is not constant for all objects, as wind resistance is dependent upon a number of factors, such as shape and material of the object.

In a vacuum, there is no wind resistance. Now, there is no force to counter gravity. Therefore, velocity continues to increase due to the constant acceleration due to the gravity force.